Domestic irons consists of a heated metal sole plate onto which water from a reservoir is dripped to generate steam, which is then emitted through holes in the sole plate. The clothes are then pressed by an action of heat and steam. This method produces a small and varying amount of steam and is really only suitable for small amounts of clothes.
An improvement has been made through the introduction of separate water reservoir and steam generators. In this embodiment, a water tank and steam generator is separate from the iron, which also consists of a heated sole plate. The generated steam is then sent down a pipe to the iron, where a constant stream of steam is then released onto the clothes. This method has the advantage of a large water tank for heavy use and a constant flow of steam. The main disadvantage is that the steam can cool down in the pipe and the system is very inefficient and takes a long time to warm up.
With the latter system, one option would be to pump water up a pipe and generate steam in the iron. However, current nichrome heating technology has a power density limitation, because if the heater becomes too hot, then it will oxidize or burn out. Thus without making the iron much larger and having a dramatic impact on the sole plate temperature, the volume of steam generation is limited. Making the heater separate from the iron allows for a large heater sub-assembly and hence a large rate of steam without the requirement for a large heater power density at the expense of heat up time and efficiency. A further disadvantage of this method is that the steam has to be re-heated at the iron and this can impact on the sole plate temperature at higher flow rates initially when the iron is cold, until the iron is at the correct working temperature. In particular, if a sole plate with poor thermal conductivity is used, then this will become a potentially large problem.
We have therefore appreciated the need for an improved iron and steam generation system.